1. Field of the Invention
The present invention relates to base stations, mobile stations, and a method of communicating.
2. Description of the Related Art
In HSDPA (High speed downlink packet access), HS-PDSCH, which carries data traffic, is fixedly determined as 3 slots (2 msecs). (See Non-patent documents 1 and 2, for example.) In other words, in HSDPA, data is transferred from Layer 2 to Layer 1 with three slots as a unit.
Allocation of transmission opportunities in HSDPA is described below.
Each UE receives HS-SCCH, and, for allocation of transmission opportunities for an own UE, subsequent HS-PDSCH is received, and HS-DSCH is decoded. In HSDPA, if each UE fails in receiving HS-SCCH, as a base station can not transmit a reception acknowledgment for HS-DSCH, DTX is detected, and HS-DSCH is retransmitted.
On the other hand, in standardizing evolved UTRA, supporting a variable-length TTI (transmission time interval) is being proposed. (See Non-patent documents 3, 4, and 5, for example.)
Non-patent document 1    TS25.211 Section 7.8
Non-patent document 2    TS25.214 Section 6A.1.1
Non-patent document 3    Motorola, R2-060122, “Layer 1 Data Transfer Formats and Definitions”, 3GPP TSG RAN WG2 #50 Sophia Antipolis, France. 9-13 Jan. 2006
Non-patent document 4    Ericsson, R2-060868, “Increased TTI Length”, 3GPP TSG-RAN Joint WG1/WG2 Athens, Greece, 27-31 Mar. 2006
Non-patent document 5    Motorola, R2-060944, “HARQ Considerations”, 3GPP TSG RAN WG2 #52 Athens, Greece, 27-31 Mar. 2006